1. Field of the Invention
The present invention relates to a wireless communication system. More particularly, the present invention relates to an apparatus and method for updating a Pairwise Master Key (PMK)/Authorization Key (AK) of a mobile station in an idle mode in a wireless communication system.
2. Description of the Related Art
A mobile station operating in a wireless communication system utilizes an idle mode in order to reduce power consumption of the mobile station. In addition, use of the idle mode by the mobile station enables resources of the wireless communication system to be more efficiently utilized.
When the mobile station is in the idle mode, context for the mobile station is transferred from a base station to a paging controller, thereby conserving resources of the base station.
Meanwhile, the mobile station possesses an Authorization Key (AK) and an encryption key that are shared with a network through an authorization procedure. The AK and the encryption key are used to facilitate secure communication. For example, the base station uses the AK and the encryption key for the authorization and the encryption of data.
To ensure security of the AK and the encryption key, the PMK/AK is updated before expiration of at least one of a timer and a counter. The timer corresponds to a survival period of the PMK/AK and the encryption key. The counter corresponds to numbers related to the AK and the encryption key.
According to the conventional art, when the mobile station is in the idle mode, the mobile station performs a security key update procedure after completion of a network re-entry procedure in order to update the PMK/AK.
Thereafter, when there is no data to communicate between the mobile station and the base station, the mobile station may perform a procedure to return to the idle mode.
The conventional PMK/AK key update procedure will be described below with reference to FIG. 1.
FIG. 1 illustrates a PMK/AK update procedure of a mobile station in an idle mode in wireless communication system according to the conventional art.
Referring to FIG. 1, when a mobile station 100 is in an idle mode 160 and when an update condition for an AK and an encryption key is satisfied, the mobile station 100 transmits a ranging request message (i.e., an AAI_RNG-REQ message) to a base station 120 to request a network re-entry in step 102.
The base station 120 transmits a context request message (i.e., a Context-REQ message) to a Paging Controller (PC)/authorization station 140 in step 122 to request the network re-entry of the mobile station 100. The PC/authorization station 140 transmits a context response message (i.e., a Context-RSP message) to the base station 120 in step 142 that includes information used for the re-entry of the mobile station 100. The base station completes the network re-entry of the mobile station 100 by transmitting a ranging response message (i.e., an AAI_RNG-RSP message) to the mobile station 100 in the step 126.
After the network re-entry procedure, a key agreement triggering occurs in step 162 triggering the update of the AK for the mobile station 100, the base station 120, and the PC/authorization station 140. The base station 120 transmits a Key Agreement MSG#1 to the mobile station 100 in step 124 and the mobile station 100 transmits a Key Agreement MSG#2 to the base station 120 in step 104.
The base station transmits an AK request message (i.e., an AK-REQ message) to the PC/authorization station 140 in step 128 to request the AK. The PC/authorization station 140 transmits an AK response message (i.e., an AK-RSP message) to the base station 120 in step 144. The base station 120 determines a new AK through a 3-way handshake process by transmitting a Key Agreement MSG#3 message to the mobile station 100 in step 130.
Hereafter, the mobile station 100 may return to idle mode when there is no data to transmit or receive.
However, there are problems with the mobile station performing the network re-entry procedure only to update the AK and then return to the idle mode. For example, power consumption of the mobile station is increased and resources of the base station are wasted.
Therefore, a need exists for an apparatus and method for updating an AK for a mobile station in an idle mode that does not increase power consumption of the mobile station and does not waste resources of the base station.